Countercurrent solvent extractor



Sept. 11, 1951 e. R. FlTTS ET AL I COUNTER CURRENT SOLVENT EXTRACTOR Filed July 2, 1947 INVENTOR. GEORGE R.F|TTs BY FRED 6. Low

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Patented Sept. 11, 1951 George R. Fitts, York, Pa., and Frederick G. Low,

Newark, Del., assignors, by direct and mesne assignments, to Read Standard Corporation, a

corporation of Delaware Application July 2, 1947, Serial N 0. 758,520

Claims. (0!. 23-270) This invention relates to a method and apparatus for continuous counter-current solvent extraction of solid materials.

It is an object of the present invention to provide a novel procedure and apparatus of greater efiiciency than those disclosed in the prior art for extracting soluble matter from solid materials containing such matter.

A further object of the invention is to provide solvent extraction apparatus of the type described embodying the counter-current flow of solvent and solvent material,that is so improved in structure and mode of operation as to be capable of more rapid and efficient extraction than prior devices.

It has been previously proposed to employ a tank having a series of adjacent extracting sections in the form of trough-shaped tubs, with a paddle Wheel in each for moving the material to be extracted through its respective section and over the common edge of a pair of adjacent sections into the next succeeding section, and causing solvent to flow from one section to the next succeeding section in a direction counter-current with respect to the direction of movement of the material being extracted. In this previous method and apparatus, the level of the solvent has been maintained a substantial distance above the common or spill edge of a pair of adjacent sections to assure a continuous flow of solvent. It is apparent that in such method and apparatus a substantial portion of the material to be extracted is carried over from one extracting section or tub to the next succeeding one while still immersed 'in the solvent, resulting in the carrying back of solvent having a greater concentration of dissolved matter into and mixing it with the solvent having a lesser concentration of dissolved matter. Since this occurs continually in each extracting section, the cumulative efiect is to materially prolong the extracting time.

It is, therefore, a more specific object of the invention to provide a novel procedure and apparatus in which carry back of solvent having a greater concentration of dissolved matter and mixing of it with solvent having a lesser concentration of dissolved matter is very materially reduced by raising the material to be extracted entirely out of contact with the solvent for sub stantially completely draining it before it is moved into the next succeeding extraction section.

In apparatus employing successive extraction sections it has been previously proposed to form a dam of material being extracted on or near the common spill edge of a pair of adjacent extracting sections tending to prevent reverse infusion of the solvent, however, since the major portion of the damwas beneaththe level ofvv the solvent, it not only carried back a substantial part of the solvent but also interferred with the free flow of solvent from one extracting section to the next. An important object of the present invention, therefore, is to provide a novel procedure and apparatus wherein not only is reverse infusion of solvent minimized but damming of the flow of solvent is eliminated permitting free flow of solvent from one extracting section to the next.

These and other objects, including improving generally on the procedures and structures previously employed in similar solvent extraction operations, will appear more fully from the following description and the accompanying drawing illustrating a preferred embodiment of the invention. In the drawing Figure 1 is a central vertical longitudinal sectional view of the improved apparatus;

Figure 2 is a sectional view of the invention taken on the line 2-2 of Figure 1;

' Figure 3 is an enlarged view of the baflle and portions ofthe adjacent extracting-sections of the improved apparatus; and

Figure 4 is a sectional view taken on the line 44 of Figure 3.

The preferred embodiment of the invention, as shown in the drawing, comprises a tank l0 provided with a plurality of adjacent troughshaped tubs or extracting sections II which extend across the entire width of the tank It and are arranged parallel one with respect to the other. The adjacent upper ends of each pair of adjacent tubs are formed with a common spill edge over which material to be extracted is passed from one tub II to the next, the series of tubs ll forming the bottom wall of an extraction chamber l2.

The tank In is provided with a top wall [3 which also forms the top wall of the extraction chamber I2. The top wall 13 is preferably provided with a plurality of inspection openings H normally closed by the covers I5.

Mounted in each of the tubs I I is a paddle wheel ll, extending the full width of the extraction chamber 12 and comprising a hub l8 which may be in the form of a drum of any suitable shape in cross section, but preferably round as shown in the drawings, and a plurality of preferably, though not necessarily, curved perforated blades Ill, The blades I9 extend the full width of the extraction chamber [2 and are spaced at equal distances about the hub l8 to which they are secured in any suitable manner. Strengthening ribs 20 either formed with or suitably secured to the blades I9 extend a distance circumferentially The hubs I8 are secured to and arranged to rotate with shafts 2I which extend through and are journaled in the sides of the tank I0. On the extensions of the shafts 2I at one side of the tank). are mounted Worm wheels 22 meshing with worms 23 on the main driving shaft 24 which is operated from a suitable source of power (not shown).

The material from which soluble matter is to be extracted is introduced into an end tub I-I of the extraction chamber I2inanysuitable manner. passes from the spout 25, which preferably extends the width of the tub II, .through -a rota'ryy metering device I6 and then through an opening 26 in the top wall I3 of chamber I2. "It'isfof course, desirable to arrange the spout or spouts 25 in such-manner asto'obtainlan' even distribution :of the material across the width of tub II. The blades I I9,which rotate in' th direction of the arrows as shown in Figure 1,-advance the materialin segregated masses from one tub to the next 'suc'ceeding tub, finally delivering 'the residue onto the lower en'd' of an endless conveyor 21 mounted in the=conveyor housing 28 which communicates with the end of the extraction chamber I2 opposite that end into which the material i introduced.

The':solvent employedin the extraction process is Introducedthrough apipe or pipes 29 into the end tub II oppositethe' point of introduction of the material to be extracted, however, it will be apparent'that if desired the solvent may be introduced into the conveyor housing 28, from whichit-will flow over the edge of and into the adjacent tub' I'I.

The'common spill edgeof adjacent tubs II is preferably though' not necessarily formed as a separable member orbafile 30 seated on a sealing strip'orzplate 3| connecting the adjacent upper ends of the arcuate shaped wall portions 32 of adjacent tubs I l. Considered in cross section, the arcuate shaped wall portions 32- are in the form of a minor-arc described about'theaxis of'the paddle wheels I! so'that during rotation of'the paddle wheels, the ends of the blades I9 will fit closelya'gainst the inner surface of the arcuate shaped wall portions 3 2-.

Incross section, the bailies 30 are preferably triangular-in shape, the sidefaces of which are preferably formed on the same radius asthe wall portions 32, so that they form continuations of the arcuate surfacesof the wall portions'32. It is obvious that the baflies 39 may be other than triangular in cross section and the side faces need not necessarily be arcuate, since the ends of the blades I9 may be provided with flexible flaps that will maintain a close lit with the side faces of the baflles 30, or if the space between the ends of the blades I9 and the side faces of the baflles is not so great as to permit an appreciable amount of--material to pass therebetween, such flaps are not necessary. Each of-the baffles 30 is'provided in its basewith recesses 33 and perforated metal strips 34 are secured in any suitable mamier, as by welding, in the recesses 33, and are Preferably curved to followthe contour of the wall portions-32 and the side faces of the baffles 30. The recesses 33 and perforated strips34 are disposed at a level substantially below the level of the axes of the paddle 'wheels I'Tbut not below the level of the lowermost portion of the drums I8,"while the'cre'st'or spill edge of the baflles'30 arearranged at approximately the same level as the'le'vel 'of the axes of-the paddle-wheels IT. The recesses 33 provide passages for the As shown in the drawings, the material- 4 flow of solvent from one trough shaped tub to the next, and the sealing strips 3| which as previously explained connect the upper ends of adijacentrtubs, form'a bottom wall forthe passages,

solvent, indicated at X in Figure 1, at substantlallythe "level'of the perforations in the strips 34. The crests or spill edges of the baffles 30 being substantially above the level X of the solvent, it is apparent that the solid material is carried upwardly by the paddle wheel blades I! out of contact with the solvent and drops over the spill "edge *of the baflles 3|) into the next succeeding tub, the direction of movement of the solid material through=the extraction chamber I2being countercurrent with respect to the direction'of flow of the'solvent. 'Sincethe perforated'metal strips 34 are 'at'an elevation at least as high as the bottom portion of the drums I8, it is evident that the level of the solvent Willjbe maintained at least ashigh as the bottom-portion-of the drums -I8,thereby preventing light particles of'materialfrom floating on the'surfa'ce ofthe solvent into the next section and assuring'positive'submersion of all the material in'the-solvent in each of the series'o'f tubs II.

The end-tub I-I opposite thesolvent'inlet pipe 29 is provided with'astrainer'or screen 35 which permits passage of the micella or solvent with its dissolved matter into the micella receiving chamber '36, formed by an extended portion of the tank I0. The micella or solvent with-its dissolvedmatteris withdrawn'from the chamber 36through pipe 31 "and-may -then be delivered to a suitable recovery plant where the soluble matter and solvent maybe separated and "collected in known manner.

The blades'lll .curv :back from the drumsIB of the pad'dlewheels IIin a generally tangential direction so that'the material falls away from the blades, as they ascend from the confines of the "tubs I I, and 'drops'into "the'next succeeding tub.

In operation'the material to be extracted drops fromtherotary valveIB into 'the space between two successive "blades I9Iof the paddle wheel H. The trailing blade pushes the material down into the solventaroun'd' the bottom of .the.tub I I, then elevates the segregated mass of material through the solventand Tfinally raises the entire segregated mass of material out of contactwith the solvent, whereupon this segregated mass of material .is substantially completely drained. The solvent that is drained from the material passes through-the perforations of the trailingblade. I9 back into the sametub II, while vthe thoroughly drained material drops from the trailing blade I9 over I the spill edge of the .baflle-43Il into the. next succeedingtub I I. This positive submersion-of the material and substantially :complete drainage is: repeat-edinw-each of the series of tubs I I, the drained material finally passing onto theeonveyor-:2I.

'Since theisegregated massesof material ar substantially ":completely .drained' of solvent before beingdelivered fromzone tub to the next succeeding tubflcarrying r back-rzofsolvent: having a' higher concentration ;of.rlissolved'imatter into solvent havinga lowerlconcentnationtofl dissolved matter is very materially reduced as compared to prior apparatus.

It is, of course, apparent that the material being extracted still retains a certain amount of the solvent-solute mixture when it passes over the baffles 33 from one tub to the next. In the description and claims it will be understood that by substantially complete drainage is meant that no substantial further amount of solvent-solute mixture will freely drip from the material being extracted. In other words, the solvent-solute mixture is not expressed from the material but is permitted to substantially completely drain by gravity from each entire segregated mass or" material before being introduced into the next succeeding extraction section.

The solvent-solute mixture retained by the material being extracted is diluted in the next succeeding extraction section with solvent containing a lower percentae of solute, the extraction process is repeated and again the material is drained before being passed on to the next extraction section. This process is repeated through the necessary number of extraction sections until the solvent-solute content of the material being extracted reaches the minimum of residual solute.

Our improved method and novel apparatus for extracting soluble matter from solid materials containing the same are capable of more rapid and efficient extraction than previously known methods and apparatus.

We claim:

1. In a countercurrent solvent extraction apparatus, a series of troughs arranged side by side and forming the bottom of an extraction chamber, each pair of adjacent troughs having their adjacent walls meeting in a common top edge portion, said adjacent walls having passageways formed in said common top edge portion and above the bottom of said troughs providing for the flow of solvent therethrough from one trough to the next to maintain the solvent at the level of said passageways and conveying means rotating in said troughs above and below the level of said passageways for moving the material through said troughs counter to the direction of flow of the solvent and above said passageways for depositing it over said common top edge portions into the next succeeding trough.

2. In a countercurrent solvent extraction apparatus, a series of troughs arranged side by side and forming the bottom of an extraction chamber, said troughs being of arcuate configuration in cross section, each pair of adjacent troughs having their adjacent walls meeting in a common top edge portion, said adjacent walls having passageways formed in said common top edge portion and above the bottom of said troughs providing for the flow of solvent therethrough from one trough to the next to maintain the solvent at the level of said passageways, means for moving material through said extraction chamber in a direction opposed to the direction of flow of said solvent, said means including a rotatable hub extending the full length of each trough with the lowermost peripheral portion of each of said hubs being below said passageways and the uppermost peripheral portion of each of said hubs being above said common top edge portion, perforated blades extending outwardly from said hubs and having their free ends move in a path in juxtaposition to the arcuate interior surface of said troughs, said blades on rotation submerging the material below the level of the 6 solvent, moving it through said troughs, raising it above said passageways and depositing it over said common top edge portions into the next succeeding trough.

3. In countercurrent solvent extraction apparatus in which material to be treated is introduced adjacent one end of the apparatus and solvent adjacent the other, a series of adjacent extracting troughs comprising walls of arcuate configuration in cros section, a plate connecting the adjacent upper edges of said arcuate walls, a baffle seated on each of said plates and provided with passageways for the flow of solvent therethrough from one trough to the next adjacent trough and conveying means rotating in said troughs for first moving the material through the solvent in said troughs and then out of contact with the solvent and over said bafiles into the next succeeding trough.

4. In countercurrent solvent extraction apparatus in which material to be treated is introduced adjacent one end of the apparatus and solvent adjacent the other, a series of adjacent extracting troughs comprising walls of arcuate configuration in cross section, a plate connecting the adjacent upper edges of said arcuate walls, a baffle seated on each of said plates, the side walls of said baffles being formed on the same radius of curvature as the radius of ourvature of said arcuate walls to form continuations thereof, said bafiles having passageways formed in the base portion thereof adjacent said plates for the flow of solvent therethrough from one trough to the next adjacent trough and conveyin means rotating in said troughs above and below the level of said passageways for moving the material through said troughs counter to the direction of flow of the solvent and above said passageways for depositing it over said baffies into the next succeeding trough.

5. In countercurrent solvent extraction apparatus in which material to be treated is introduced adjacent one end of the apparatus and solvent adjacent the other, a series of adjacent extracting troughs comprising walls of arcuate configuration in cross section, a plate connecting the adjacent upper edges of said arcuate walls, a bafile seated on each of said plates, said baffles having recesses provided in the bases thereof penetrating said baffles, perforated strips mounted in the recesses of said baffles and providing for the flow of solvent therethrough from one trough to the next adjacent trough, said 'bafiles and perforated strips being formed on the same radius of curvature as the radius of curvature of said arcuate walls and rotating paddle wheels in said troughs for moving said material through said solvent counter to the direction of flow of the solvent and above said perforated strips for depositing it over said baffles into the next succeeding trough.

GEORGE R. FITTS.

FREDERICK G. LOW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 471,995 Gschwind Mar. 29, 1892 1,628,787 Kennedy May 17, 1927 2,227,605 Swallen et al Jan. 7, 1941 2,405,105 Kennedy July 30, 1946 

1. IN A COUNTERCURRENT SOLVENT EXTRACTION APPARATUS, A SERIES OF TROUGHS ARRANGED SIDE BY SIDE AND FORMING THE BOTTOM OF AN EXTRACTION CHAMBER, EACH PAIR OF ADJACENT TROUGHS HAVING THEIR ADJACENT WALLS MEETING IN A COMMON TOP EDGE PORTION, SAID ADJACENT WALLS HAVING PASSAGEWAYS FORMED IN SAID COMMON TOP EDGE PORTION AND ABOVE THE BOTTOM OF SAID TROUGHS PROVIDING FOR THE FLOW OF SOLVENT THERETHROUGH FROM ONE TROUGH TO THE NEXT TO MAINTAIN THE SOLVENT AT THE LEVEL OF SAID PASSAGEWAYS AND CONVEYING MEANS ROTATING IN SAID TROUGHS ABOVE AND BELOW THE LEVEL OF SAID PASSAGEWAYS FOR MOVING THE MATERIAL THROUGH SAID TROUGHS COUNTER TO THE DIRECTION OF FLOW OF THE SOLVENT AND ABOVE SAID PASSAGEWAYS FOR DEPOSITING IT OVER SAID COMMON TOP EDGE PORTIONS INTO THE NEXT SUCCEEDING TROUGH. 